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Peter Anvin" , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Emanuele Giuseppe Esposito Subject: [PATCH 4/4] KVM: use signals to abort enter_guest/blocking and retry Date: Sat, 22 Oct 2022 11:48:19 -0400 Message-Id: <20221022154819.1823133-5-eesposit@redhat.com> In-Reply-To: <20221022154819.1823133-1-eesposit@redhat.com> References: <20221022154819.1823133-1-eesposit@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Spam-Status: No, score=-2.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1747403633714788400?= X-GMAIL-MSGID: =?utf-8?q?1747403633714788400?= Once a vcpu exectues KVM_RUN, it could enter two states: enter guest mode, or block/halt. Use a signal to allow a vcpu to exit the guest state or unblock, so that it can exit KVM_RUN and release the read semaphore, allowing a pending KVM_KICK_ALL_RUNNING_VCPUS to continue. Note that the signal is not deleted and used to propagate the exit reason till vcpu_run(). It will be clearead only by KVM_RESUME_ALL_KICKED_VCPUS. This allows the vcpu to keep try entering KVM_RUN and perform again all checks done in kvm_arch_vcpu_ioctl_run() before entering the guest state, where it will return again if the request is still set. However, the userspace hypervisor should also try to avoid continuously calling KVM_RUN after invoking KVM_KICK_ALL_RUNNING_VCPUS, because such call will just translate in a back-to-back down_read() and up_read() (thanks to the signal). Signed-off-by: Emanuele Giuseppe Esposito --- arch/x86/include/asm/kvm_host.h | 2 ++ arch/x86/kvm/x86.c | 8 ++++++++ virt/kvm/kvm_main.c | 21 +++++++++++++++++++++ 3 files changed, 31 insertions(+) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index aa381ab69a19..d5c37f344d65 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -108,6 +108,8 @@ KVM_ARCH_REQ_FLAGS(30, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP) #define KVM_REQ_MMU_FREE_OBSOLETE_ROOTS \ KVM_ARCH_REQ_FLAGS(31, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP) +#define KVM_REQ_USERSPACE_KICK \ + KVM_ARCH_REQ_FLAGS(32, KVM_REQUEST_WAIT) #define CR0_RESERVED_BITS \ (~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \ diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b0c47b41c264..2af5f427b4e9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10270,6 +10270,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) } if (kvm_request_pending(vcpu)) { + if (kvm_test_request(KVM_REQ_USERSPACE_KICK, vcpu)) { + r = -EINTR; + goto out; + } if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) { r = -EIO; goto out; @@ -10701,6 +10705,10 @@ static int vcpu_run(struct kvm_vcpu *vcpu) r = vcpu_block(vcpu); } + /* vcpu exited guest/unblocked because of this request */ + if (kvm_test_request(KVM_REQ_USERSPACE_KICK, vcpu)) + return -EINTR; + if (r <= 0) break; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index ae0240928a4a..13fa7229b85d 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3431,6 +3431,8 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu) goto out; if (kvm_check_request(KVM_REQ_UNBLOCK, vcpu)) goto out; + if (kvm_test_request(KVM_REQ_USERSPACE_KICK, vcpu)) + goto out; ret = 0; out: @@ -4668,6 +4670,25 @@ static long kvm_vm_ioctl(struct file *filp, r = kvm_vm_ioctl_enable_cap_generic(kvm, &cap); break; } + case KVM_KICK_ALL_RUNNING_VCPUS: { + /* + * Notify all running vcpus that they have to stop. + * Caught in kvm_arch_vcpu_ioctl_run() + */ + kvm_make_all_cpus_request(kvm, KVM_REQ_USERSPACE_KICK); + + /* + * Use wr semaphore to wait for all vcpus to exit from KVM_RUN. + */ + down_write(&memory_transaction); + up_write(&memory_transaction); + break; + } + case KVM_RESUME_ALL_KICKED_VCPUS: { + /* Remove all requests sent with KVM_KICK_ALL_RUNNING_VCPUS */ + kvm_clear_all_cpus_request(kvm, KVM_REQ_USERSPACE_KICK); + break; + } case KVM_SET_USER_MEMORY_REGION: { struct kvm_userspace_memory_region kvm_userspace_mem;